What are the diagnostic criteria and treatment options for Acquired Immune Deficiency Syndrome (AIDS)?

AIDS Diagnosis and Management

AIDS is diagnosed when an HIV-infected person has a CD4+ T-lymphocyte count <200 cells/μL or develops specific opportunistic infections (such as Pneumocystis carinii pneumonia, thrush, or unexplained fever >37.8°C for ≥2 weeks), regardless of CD4 count. 1

Diagnostic Criteria for AIDS

The progression from HIV infection to AIDS is defined by immunologic and clinical parameters:

CD4+ Count Thresholds

• CD4+ count <200 cells/μL automatically defines AIDS, even in asymptomatic patients 1
• Patients with CD4+ counts 200-500 cells/μL are at increased risk for HIV-related symptoms but do not meet AIDS criteria unless specific conditions develop 1
• CD4+ count >500 cells/μL with thrush or unexplained fever (>37.8°C for ≥2 weeks) also indicates progression to complicated HIV disease requiring intensive management 1

Clinical AIDS-Defining Conditions

Beyond CD4 thresholds, specific opportunistic infections establish an AIDS diagnosis 1:

• Pneumocystis carinii pneumonia (PCP)
• Oral or esophageal candidiasis (thrush)
• Tuberculosis
• Toxoplasmic encephalitis
• Disseminated Mycobacterium avium complex disease

Initial HIV Diagnostic Testing

Testing Algorithm

Begin with enzyme immunoassay (EIA) screening, followed by Western blot or immunofluorescence assay (IFA) confirmation for all reactive results. 1, 2

• Informed consent (written in some states) is mandatory before testing 1, 2
• All reactive screening tests must be confirmed before disclosing positive results to avoid false-positive diagnoses 2
• If confirmatory testing is negative or indeterminate, repeat testing on a specimen collected 4 weeks later 2

Critical Window Period Caveat

Antibody tests cannot rule out infection acquired within the previous 6 months, as HIV antibody is detectable in ≥95% of patients only after 6 months of infection 2, 3. Acute infection within 2-4 weeks may yield completely negative results despite active viral replication 3.

Comprehensive Initial Evaluation for HIV-Positive Patients

Once HIV infection is confirmed, the following evaluation determines disease stage and treatment needs 1:

Essential Laboratory Testing

• CD4+ T-lymphocyte count (absolute number preferred for clinical decision-making, though percentage is more consistent) 1
• HIV viral load (plasma RNA) 1
• Complete blood count and platelet count 1
• Comprehensive metabolic panel 1
• Toxoplasma antibody test 1
• Hepatitis B viral markers 1
• Syphilis serology 1

Tuberculosis Screening

• Tuberculin skin test (TST/PPD) by Mantoux method 1
• ≥5 mm induration is considered positive in HIV-infected persons (lower threshold than general population) 1
• Anergy testing with delayed-type hypersensitivity antigens (Candida, mumps, or tetanus toxoid), though its usefulness is controversial 1
• Chest radiograph 1

Clinical History and Physical Examination

• Detailed sexual and substance abuse history 1
• Review of systems for HIV-related symptoms: fever, weight loss, diarrhea, cough, shortness of breath, oral lesions 1
• Complete physical examination 1
• For women: gynecologic examination, testing for N. gonorrhoeae and C. trachomatis, Pap smear, and wet mount of vaginal secretions 1

Psychosocial Assessment

• Behavioral risk factors for HIV transmission 1
• Partner notification needs 1
• Mental health screening for severe psychological distress requiring urgent referral 1

Treatment Initiation Based on Disease Stage

Immediate Interventions for AIDS (CD4 <200 cells/μL)

Patients with AIDS require urgent referral to comprehensive HIV care facilities with specialty resources and hospitalization access. 1

• Antiretroviral therapy initiation 1
• Prophylaxis for opportunistic infections (PCP, toxoplasmic encephalitis, disseminated MAC, tuberculosis) 1
• Evaluation and treatment of active opportunistic infections 1

Preventive Therapy for Tuberculosis

• HIV-positive persons with PPD ≥5 mm induration should receive isoniazid preventive therapy (10 mg/kg daily, maximum 300 mg) after excluding active TB 1
• Anergic persons with ≥10% estimated risk of tuberculous infection should also be considered for preventive therapy 1

Vaccinations

• Hepatitis B vaccination for those without hepatitis B markers 1
• Annual influenza vaccination 1
• Pneumococcal vaccination 1

Special Diagnostic Considerations

Infants and Children

For infants <15 months born to HIV-positive mothers, diagnosis must be based on virologic testing (HIV DNA or RNA PCR), not antibody testing, as maternal antibodies cross the placenta and persist 2, 3.

HIV-2 Testing

Consider HIV-2 testing in 2, 3:

• Persons from endemic regions (West Africa, Portugal, France, India) or their sexual partners
• Patients with clinical evidence of HIV disease but negative HIV-1 antibody tests
• Unusual indeterminate Western blot patterns (gag plus pol bands without env bands)

Common Pitfalls to Avoid

• Never disclose a positive HIV diagnosis based on screening tests alone without confirmatory testing 2
• Do not rely on antibody testing to exclude recent infection (within 6 months) 2, 3
• Do not use antibody tests for infant diagnosis in children <15 months 2, 3
• Do not delay urgent referral for patients with symptoms suggesting advanced disease (fever, weight loss, thrush, respiratory symptoms) 1
• Avoid fragmented care by establishing comprehensive treatment plans with coordinated services 1